1. Field of the Invention
This invention relates to a photoelectric smoke detector which operates on the scattered light principle. In accordance with this principle a light source and photosensor are provided within a detector chamber, the photosensor being placed at an angle to the light beam such that it is normally unilluminated by such beam, the detection chamber having air entry ports that restrict ambient light. Smoke particles entering the smoke chamber interrupt the light beam, thereby scattering light onto the photosensor.
2. Background Information
The present invention is related to an invention described and claimed in U.S. Pat. No. 4,654,644, assigned to the assignee of the present invention. That co-pending application claims circuitry involved with the smoke detector herein described. The details of the circuitry of the co-pending application are herein incorporated by reference.
Light scattering smoke detectors have been known before and in order to place the present invention in its proper context, reference may be made to the following U.S. Pat. Nos. 4,168,438; 4,206,366 and 4,216,377.
It will be apparent from a reading of these three patents that a paramount concern has been to prevent light reflection from the detection chamber walls from producing an undesirable inherent noise level, thus reducing the sensitivity and reliability of the detector. Likewise, it is of fundamental concern to prevent light from the ambient from entering the dark detection chamber.
Whatever the merits of the devices described in the above cited references, they do not fulfill the purposes and objectives in accordance with the present invention.